add test for computing mud

Author: yucongalicechen

tests/test_mud_calculator.py

@@ -0,0 +1,22 @@
+from pathlib import Path
+
+import numpy as np
+import pytest
+
+from diffpy.labpdfproc.mud_calculator import _extend_x_and_convolve, compute_mud
+
+
+def test_compute_mud(tmp_path):
+    diameter, slit_width, x0, I0, mud, slope = 1, 0.1, 0, 1e5, 3, 0
+    x_data = np.linspace(-1, 1, 50)
+    convolved_I_data = _extend_x_and_convolve(x_data, diameter, slit_width, x0, I0, mud, slope)
+
+    directory = Path(tmp_path)
+    file = directory / "testfile"
+    with open(file, "w") as f:
+        for x, I in zip(x_data, convolved_I_data):
+            f.write(f"{x}\t{I}\n")
+
+    expected_mud = 3
+    actual_mud = compute_mud(file)
+    assert actual_mud == pytest.approx(expected_mud, rel=0.1, abs=0.1)